A veteran herself of the anti-apartheid struggle, Winnie Mandela died on Monday afternoon, her personal assistant said.

"She died after a long illness, for which she had been in and out of hospital since the start of the year," Victor Dlamini, a family spokesperson, said in a statement on Monday.

"She succumbed peacefully in the early hours of Monday afternoon surrounded by her family and loved ones."

Born in the Eastern Cape's Bizana town in 1936, Nomzamo Winifred Madikizela moved to Johannesburg in 1953 to pursue studies in social work before meeting Nelson Mandela, her future husband, who was then an anti-apartheid campaigner.

Winnie developed a reputation as an uncompromising opponent of South Africa's racial segregation system.

Winnie Mandela, centre, was for long a powerful figure in the governing ANC [AP]

Al Jazeera's Catherine Soi, reporting from Johannesburg, said Winnie Mandela's family described her as a strong woman who relentlessly fought for the majority black population's rights.

"Her family gave a very moving tribute about how they said she really is the face of the struggle against apartheid," she said.

"She wasn't married very long to Nelson Mandela before he was imprisoned, so she was very much his face and his voice to the outside world. And she took that role very seriously."

Winnie was married to Nelson Mandela from 1958 to 1996, although for almost three decades of that time they were separated due to his imprisonment.

Despite their separation two years after his release in 1990, and their divorce in 1996, she kept his surname and maintained ties with him.